#include <iostream>
using namespace std;

const float PI = 3.1416;

void main()
{
	int iType;
	float radius, a, b, area;
	
	cout << "圖形的類型為?(1-圓形 2-長方形 3-正方形):";
	cin >> iType;
	switch(iType)
	{
	case 1:
		cout << "圓的半徑為：";
		cin >> radius;
		area = PI * radius * radius;
		cout<<"面積為："<<area<<endl;
		break;
	case 2:
		cout << "矩形的長為：";
		cin >> a;
		cout << "矩形的寬為：";
		cin >> b;
		area = a * b;
	    cout<<"面積為："<<area<<endl;
		break;
	case 3:
		cout << "正方形的邊長為：";
		cin >> a;
		area = a * a;
    	cout<<"面積為："<<area<<endl;
		break;
	default:
		cout << "不是合法的輸入值!"<<endl;
	}
}